JP2013139316A - Lifting device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lifting device capable of reducing operating shocks or others when beginning to lower lifted articles even without using a high cost valve whose control is complicated.SOLUTION: A lifting device 1 has a pilot check valve 9 arranged between a hydraulic pump motor 5 and a lift cylinder 3 and allowing or blocking flow of operating oil from the lift cylinder 3 to the hydraulic pump motor 5 according to presence or absence of a pilot pressure and an orifice 27 arranged between the hydraulic pump motor 5 and a tank 4 and squeezing the operating oil discharged from the hydraulic pump motor 5. The pilot pressure is generated in an upstream side of the orifice 27 (between the hydraulic pump motor 5 and the orifice 27) when rotating the hydraulic pump motor 5 in a fork lowering direction. A pilot tube channel 18 for supplying the generated pilot pressure to the pilot check valve 9 is connected between the upstream side of the orifice 27 and the pilot check valve 9.

Description

  The present invention relates to a lifting device that lifts and lowers a lift by hydraulic drive of a hydraulic cylinder.

  For example, in a lifting device for a forklift, when a fork (lifting object) is moved down, a cargo handling regeneration that generates power by returning hydraulic oil from a hydraulic cylinder for lifting the fork to a hydraulic pump using the weight of the load is known. is there. During such cargo recovery, when a switching valve disposed on the oil passage between the hydraulic pump and the hydraulic cylinder is opened, an operation shock or vibration is generated due to a pressure difference between the upstream side and the downstream side of the switching valve. When an electromagnetic proportional valve is used as the switching valve, the switching valve gradually opens, so that the fork descending operation is stabilized.

  As a conventional lifting device, for example, as described in Patent Documents 1 and 2, when the lowering of the fork is instructed, the hydraulic pump is rotated in the upward direction of the fork, and then the electromagnetic switching valve is moved from the raised position. It is known to switch to the lowered position and rotate the hydraulic pump in the fork descending direction.

JP 2008-63072 A JP 2008-7258 A

  In the above prior art, when the fork starts to descend, it is possible to reduce the occurrence of operation shock and vibration due to the pressure difference between the upstream side and the downstream side of the switching valve. However, since an electromagnetic valve or an electromagnetic proportional valve is used as the switching valve, there are problems such as high cost and complicated control.

  The objective of this invention is providing the raising / lowering apparatus which can reduce the operation shock etc. at the time of the descent | fall start of a raising / lowering object, without using a valve with high cost and complicated control.

  The present invention relates to a lifting device that lifts and lowers an elevator by hydraulic drive of a hydraulic cylinder, a tank that stores hydraulic oil, a hydraulic pump that sucks hydraulic oil from the tank and supplies hydraulic oil to the hydraulic cylinder, a hydraulic pump, and hydraulic pressure A pilot check valve that is arranged on the oil passage between the cylinder and allows or shuts off the flow of hydraulic oil from the hydraulic cylinder to the hydraulic pump according to the presence or absence of pilot pressure, and on the oil passage between the hydraulic pump and the tank And a pilot pressure generating means for generating a pilot pressure when the hydraulic pump is rotated in the descending direction of the lift, and a pilot pressure for supplying the pilot pressure generated by the pilot pressure generating means to the pilot check valve And a supply path.

  In such a lifting device of the present invention, when the hydraulic pump is rotated in the downward direction of the lift when the lift is lowered, the pilot pressure is generated on the oil path between the hydraulic pump and the tank by the pilot pressure generating means. A pressure is generated, and the pilot pressure is supplied to the pilot check valve through the pilot pressure supply path. Accordingly, the pilot check valve is opened, and the flow of hydraulic oil from the hydraulic cylinder to the hydraulic pump is allowed, so that the lift is lowered. At this time, for example, by generating an appropriate pilot pressure according to the number of rotations of the hydraulic pump, the pilot check valve is prevented from opening suddenly. can do. As a result, it is not necessary to use a valve having a high cost and complicated control, such as an electromagnetic valve or an electromagnetic proportional valve.

  Preferably, the pilot check valve includes a plunger that opens and closes a flow path between the hydraulic pump and the hydraulic cylinder, a first spring that biases the plunger in a direction to close the flow path between the hydraulic pump and the hydraulic cylinder, And a poppet that pushes the plunger to open a flow path between the hydraulic pump and the hydraulic cylinder when pilot pressure is supplied.

  In this case, when the pilot pressure is supplied to the pilot check valve, the poppet pushes the plunger, so that the plunger moves against the urging force of the first spring, and the flow between the hydraulic pump and the hydraulic cylinder. Since the path is opened, hydraulic fluid flows from the hydraulic cylinder to the hydraulic pump. Therefore, a pilot check valve that can be opened and closed according to the presence or absence of the pilot pressure can be easily configured.

  In this case, preferably, the pilot check valve further includes a second spring that biases the poppet to the opposite side of the plunger.

  In this case, when the pilot pressure is supplied to the pilot check valve, the poppet pushes the plunger against the urging force of the second spring, so that the poppet moves gradually, and the hydraulic pump, the hydraulic cylinder, It is sufficiently prevented that the flow path between them is suddenly opened. Thereby, the operation shock and vibration at the time of the descent start of the raising / lowering object can be further reduced.

  Preferably, the pilot pressure generating means is an orifice that throttles hydraulic oil from the hydraulic pump, and the pilot pressure supply path is connected between the upstream side of the orifice and the pilot check valve.

  In this case, a pilot pressure is generated on the upstream side of the orifice due to the pressure difference between the upstream side and the downstream side of the orifice. By using such an orifice, the configuration of the pilot pressure generating means can be simplified.

  The pilot pressure generating means is a pilot on-off valve that can be switched between an open position that allows the flow of hydraulic oil from the hydraulic pump to the tank and a closed position that blocks the flow of hydraulic oil from the hydraulic pump to the tank. The pilot on-off valve has a spool and a spring that urges the spool to be held at the closed position, and is spooled between the open position and the closed position in accordance with the pressure between the hydraulic pump and the pilot on-off valve. The pilot pressure supply path may be connected between the upstream side of the pilot on-off valve and the pilot check valve.

  In this case, when the hydraulic pump is rotated in the descending direction of the elevating object while the pilot on-off valve is in the closed position, a pilot pressure is generated between the hydraulic pump and the pilot on-off valve by the spring. By using such a pilot on-off valve, the pilot pressure can be generated with almost no influence from the outside air temperature or the like.

  ADVANTAGE OF THE INVENTION According to this invention, even if it does not use a valve with high cost and complicated control, the operation shock etc. at the time of the descent | fall start of a raising / lowering object can be reduced, and the descent | fall operation | movement of a raising / lowering object can be stabilized.

1 is a system configuration diagram showing a first embodiment of a lifting device according to the present invention. It is sectional drawing which shows the structure of the pilot check valve shown in FIG. It is a system block diagram which shows 2nd Embodiment of the raising / lowering apparatus which concerns on this invention. It is sectional drawing which shows the structure of the pilot on-off valve shown in FIG.

  DESCRIPTION OF EMBODIMENTS Hereinafter, preferred embodiments of a lifting device according to the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a system configuration diagram showing a first embodiment of a lifting apparatus according to the present invention. In the figure, a lifting device 1 according to the present embodiment is a device that is mounted on a forklift such as a picking lift and lifts a fork 2 that is a lifted object.

  The lifting device 1 includes a lift cylinder 3, a tank 4, a hydraulic pump motor 5, a hydraulic pipe 6 that connects one flow port 5 a of the hydraulic pump motor 5 and a bottom chamber 3 a of the lift cylinder 3, and a hydraulic pump motor. 5 and a hydraulic pipe 7 for connecting the other circulation port 5b and the tank 4 to each other. The lift cylinder 3 is a hydraulic cylinder that moves the fork 2 up and down by hydraulic drive. The tank 4 stores hydraulic oil.

  The hydraulic pump motor 5 sucks up the hydraulic oil from the tank 4 and supplies the hydraulic oil to the bottom chamber 3 a of the lift cylinder 3. The hydraulic pump motor 5 can rotate in both directions. The flow ports 5a and 5b of the hydraulic pump motor 5 become suction ports or discharge ports depending on the flow direction of the hydraulic oil.

  An electric motor 8 that functions as an electric motor or a generator is connected to the hydraulic pump motor 5. The electric motor 8 functions as an electric motor when the hydraulic pump motor 5 operates as a hydraulic pump, and functions as a generator when the hydraulic pump motor 5 operates as a hydraulic motor.

  A pilot check valve 9 is disposed in the hydraulic pipe 6. The pilot check valve 9 permits the flow of hydraulic oil from the hydraulic pump motor 5 to the lift cylinder 3 and prevents the flow of hydraulic oil from the lift cylinder 3 to the hydraulic pump motor 5 when no pilot pressure is applied. When the pilot pressure is applied, the valve permits the flow of hydraulic oil from the hydraulic pump motor 5 to the lift cylinder 3 and the flow of hydraulic oil from the lift cylinder 3 to the hydraulic pump motor 5.

  The structure of the pilot check valve 9 is shown in FIG. In FIG. 2, the pilot check valve 9 has a valve body 10, an upper lid portion 11 provided on the upper portion of the valve body 10, and a lower lid portion 12 provided on the lower portion of the valve body 10. . In the valve body 10, a flow path space 13 and main flow paths 14 and 15, a pilot flow path 16 and a drain flow path 17 communicating with the flow path space 13 are formed. The main flow path 14 is connected to the lift cylinder 3 side of the hydraulic pipe 6, and the main flow path 15 is connected to the hydraulic pump motor 5 side of the hydraulic pipe 6. The pilot channel 16 is connected to a pilot pipeline 18 (see FIG. 1) described later. The drain flow path 17 is connected to the tank 4 via a drain pipe line 19 (see FIG. 1).

  A plunger 20 that opens and closes the main flow paths 14 and 15 is disposed in the flow path space 13. Between the plunger 20 and the upper lid portion 11, a spring 21 that biases toward the plunger 20 is disposed. The plunger 20 is normally in a position to close the main flow paths 14 and 15 by the biasing force of the spring 21 (see FIG. 2).

  Further, a poppet 22 that pushes the plunger 20 to open the main flow paths 14 and 15 when the pilot pressure is supplied to the pilot flow path 16 between the plunger 20 and the lower lid portion 12 in the flow path space 13. Is arranged. The poppet 22 includes a base portion 22a and a rod portion 22b extending from the base portion 22a toward the plunger 20 side. The rod portion 22b slidably penetrates a partition 23 disposed between the upper lid portion 11 and the lower lid portion 12. Between the base portion 22a and the partition 23, a spring 24 that biases toward the base portion 22a side (the opposite side of the plunger 20) is disposed.

  The pilot channel 16 is formed so as to be able to communicate with the channel space 13 in the lower lid portion 12. The drain channel 17 is formed so as to be able to communicate with the channel space 13 between the base portion 22a and the partition 23. The poppet 22 is normally in a position where the plunger 20 is not pushed by the biasing force of the spring 24 (see FIG. 2).

  Returning to FIG. 1, the hydraulic pipe 7 allows the flow of hydraulic oil from the tank 4 to the flow port 5 b of the hydraulic pump motor 5, and the flow of hydraulic oil from the flow port 5 b of the hydraulic pump motor 5 to the tank 4. A check valve 25 is provided to shut off.

  A hydraulic pipe 26 is connected in parallel with the hydraulic pipe 7 between the flow port 5 b of the hydraulic pump motor 5 and the tank 4. The hydraulic pipe 26 is provided with an orifice 27 for restricting the hydraulic oil discharged from the flow port 5 b of the hydraulic pump motor 5. As a result, a pressure difference is generated between the upstream side and the downstream side of the orifice 27 in the hydraulic pipe 26. Accordingly, when hydraulic oil is discharged from the flow port 5b of the hydraulic pump motor 5 by rotating the hydraulic pump motor 5 in the fork lowering direction, the upstream side of the orifice 27 (between the hydraulic pump motor 5 and the orifice 27). A pilot pressure is generated at this point. That is, the orifice 27 constitutes a pilot pressure generating means for generating a pilot pressure when the hydraulic pump motor 5 is rotated in the fork lowering direction.

  Between the upstream side of the orifice 27 in the hydraulic piping 26 and the pilot flow path 16 of the pilot check valve 9, a pilot line 18 (for supplying the pilot pressure generated on the upstream side of the orifice 27 to the pilot check valve 9 ( Are connected).

  A hydraulic pipe 28 is connected between the circulation port 5 a of the hydraulic pump motor 5 and the tank 4. The hydraulic pipe 28 has a check valve that allows the flow of hydraulic oil from the tank 4 to the flow port 5a of the hydraulic pump motor 5 and blocks the flow of hydraulic oil from the flow port 5a of the hydraulic pump motor 5 to the tank 4. 29 is provided.

  In addition, the lifting device 1 includes a lift operation lever 30 for instructing a lifting operation of the fork 2 and a controller 31. The controller 31 controls the electric motor 8 to rotate the hydraulic pump motor 5 in the fork raising direction when the lift operation lever 30 performs a fork raising operation instruction operation. When the instruction operation is performed, the electric motor 8 is controlled to rotate the hydraulic pump motor 5 in the fork lowering direction.

  In the lifting device 1 configured as described above, when the fork 2 is raised, the hydraulic pump motor 5 is rotated in the fork raising direction under the control of the controller 31. Then, the hydraulic oil sucked up from the tank 4 by the hydraulic pump motor 5 is sent to the main flow path 15 of the pilot check valve 9. Then, when the hydraulic oil pushes the plunger 20 against the biasing force of the spring 21, the main flow paths 14 and 15 are opened, and the hydraulic oil is supplied to the bottom chamber 3 a of the lift cylinder 3. As a result, the fork 2 is raised by the extension of the lift cylinder 3. At this time, the lift cylinder 3 is extended while adjusting the speed according to the rotational speed of the hydraulic pump motor 5. At this time, the hydraulic pump motor 5 operates as a hydraulic pump.

  On the other hand, when the fork 2 starts to descend, the hydraulic pump motor 5 is rotated in the fork descending direction under the control of the controller 31. Then, the hydraulic oil discharged from the flow port 5b of the hydraulic pump motor 5 passes through the orifice 27, so that the upstream side of the orifice 27 is pressurized and a pilot pressure is established. At this time, since the hydraulic oil in the tank 4 is supplied to the hydraulic pump motor 5 through the hydraulic piping 28, the flow port 5a side of the hydraulic pump motor 5 does not become negative pressure.

  When the pilot pressure is established upstream of the orifice 27, the pilot pressure is supplied to the pilot flow path 16 of the pilot check valve 9 through the pilot pipe line 18. Then, the poppet 22 moves toward the plunger 20 against the urging force of the spring 24 and pushes the plunger 20, thereby opening the main flow paths 14 and 15.

  Here, the displacement of the poppet 22 depends on the pilot pressure, and the pilot pressure depends on the flow rate of the hydraulic oil passing through the orifice 27, that is, the rotational speed of the hydraulic pump motor 5. Since it is necessary to suppress an operation shock when the fork 2 starts to descend, it is preferable to suppress the rotational speed of the hydraulic pump motor 5 and gradually increase it. Thereby, the pilot pressure given to the pilot flow path 16 becomes high gradually. In addition, a spring 24 that biases toward the base portion 22a is disposed between the base portion 22a of the poppet 22 and the partition 23. Accordingly, when the pilot pressure is applied to the pilot flow path 16, the poppet 22 gradually moves toward the plunger 20 side. As described above, since the plunger 20 gradually moves to the upper lid 11 side, the main flow paths 14 and 15 are not suddenly opened.

  When the main flow paths 14 and 15 are opened, the lift cylinder 3 contracts due to the fork 2 being lowered by its own weight. Then, hydraulic oil (return oil) discharged from the bottom chamber 3 a of the lift cylinder 3 is sucked into the hydraulic pump motor 5 through the pilot check valve 9. At this time, the hydraulic pump motor 5 operates as a hydraulic motor using the hydraulic oil discharged from the bottom chamber 3a as a driving force. As a result, the electric motor 8 functions as a generator, and the electric power generated by the electric motor 8 is stored in a battery (not shown). That is, when the fork 2 is lowered, the cargo handling regeneration operation is performed.

  When the fork 2 descends and stops, the rotation of the hydraulic pump motor 5 is stopped under the control of the controller 31. As a result, the pressure on the upstream side of the orifice 17, that is, the pressure in the pilot flow path 16 of the pilot check valve 9 decreases, and the pilot pressure is released. For this reason, the poppet 22 quickly moves to the lower lid portion 12 side by the biasing force of the spring 24, and the plunger 20 quickly moves to the poppet 22 side by the biasing force of the spring 21. 15 are immediately closed. Thereby, since the flow of the hydraulic oil from the lift cylinder 3 to the hydraulic pump motor 5 is interrupted, the operation of the lift cylinder 3 is stopped.

  As described above, in the present embodiment, the pilot check valve 9 that opens and closes depending on the presence or absence of the pilot pressure is provided on the oil passage between the lift cylinder 3 and the hydraulic pump motor 5, and the hydraulic pump motor 5 and the tank 4. Is provided with an orifice 27 for generating a pilot pressure when the hydraulic pump motor 5 is rotated in the fork lowering direction, and the generated pilot pressure is applied to the pilot check valve 9 through the pilot line 18. To do. Therefore, when lowering the fork 2, the hydraulic pump motor 5 is rotated in the fork lowering direction so that the poppet 22 of the pilot check valve 9 gradually moves toward the plunger 20 as described above, and the plunger 20 is moved. The main channels 14 and 15 are prevented from being opened suddenly. As a result, it is possible to reduce the occurrence of operational shocks and vibrations when the fork 2 starts to descend.

  As a result, expensive and complicated valves such as an electromagnetic valve and an electromagnetic proportional valve are not required. Further, the controller 31 controls only the electric motor 8 and does not need to control the valve. As described above, it is possible to stabilize the lowering operation of the fork 2 while simplifying the configuration and processing of the lifting device 1.

  Further, since the pilot pressure is generated when the hydraulic pump motor 5 is rotated in the fork lowering direction by the simple configuration of the orifice 27, it is further advantageous in terms of cost.

  FIG. 3 is a system configuration diagram showing a second embodiment of the lifting device according to the present invention. In the figure, the same or equivalent elements as those in the first embodiment are denoted by the same reference numerals, and the description thereof is omitted.

  In the figure, the lifting device 1 of the present embodiment includes a pilot on-off valve 40 instead of the orifice 27 described above. The pilot open / close valve 40 is disposed in the hydraulic pipe 26 described above. The pilot on-off valve 40 shuts off the flow of hydraulic fluid from the flow port 5b of the hydraulic pump motor 5 to the tank 4 from the open position 40a that allows the flow of hydraulic fluid from the flow port 5b of the hydraulic pump motor 5 to the tank 4. The valve is switched between the closed position 40b.

  The pilot on-off valve 40 has a valve body 41 as shown in FIG. The valve main body 41 is formed with a spool accommodating portion 43 that accommodates the spool 42, discharge passages 44 and 45, and pilot passages 46 and 47 that communicate with the spool accommodating portion 43. The discharge passage 44 is connected to the hydraulic pump motor 5 side of the hydraulic pipe 26, and the discharge passage 45 is connected to the tank 4 side of the hydraulic pipe 26. The pilot channel 46 is formed so as to communicate one side portion of the spool housing portion 43 with the discharge channel 44, and the pilot channel 47 communicates with the other side portion of the spool housing portion 43 and the discharge channel 45. It is formed to do. A spring 48 that urges the spool 42 to be held at the closed position 40b is disposed on the side of the spool accommodating portion 43 that communicates with the pilot flow path 47.

  The pilot on-off valve 40 is normally in the closed position 40b (see FIG. 3) due to the force of the spring 48. When the pressure of the pilot flow path 46 reaches a predetermined pressure, the force of the spring 48 is overcome and the closed position 40b is opened to the open position 40a. Can be switched to. At this time, when hydraulic oil is discharged from the flow port 5b of the hydraulic pump motor 5 by rotating the hydraulic pump motor 5 in the fork lowering direction with the pilot on / off valve 40 in the closed position 40b, the pilot on / off valve Pilot pressure is generated upstream of 40 (between the hydraulic pump motor 5 and the pilot on-off valve 40). That is, the pilot on-off valve 40 constitutes a pilot pressure generating means for generating a pilot pressure when the hydraulic pump motor 5 is rotated in the fork lowering direction.

  Between the upstream side of the pilot on-off valve 40 and the pilot check valve 9 in the hydraulic pipe 26, the pilot pipe 18 for supplying the pilot pressure generated on the upstream side of the pilot on-off valve 40 to the pilot check valve 9. Is connected.

  In the elevating device 1 as described above, when the fork 2 starts to descend, the hydraulic pump motor 5 is rotated in the fork descending direction under the control of the controller 31. Then, the hydraulic oil discharged from the flow port 5b of the hydraulic pump motor 5 is supplied to the pilot flow path 46 of the pilot on-off valve 40 and pushes the spool 42, so that the upstream side of the pilot on-off valve 40 is pressurized by the spring 48. Thus, a pilot pressure is established upstream of the pilot on-off valve 40. Then, the pilot pressure is supplied to the pilot flow path 16 of the pilot check valve 9 through the pilot pipe line 18.

  Accordingly, as in the first embodiment, the poppet 22 of the pilot check valve 9 moves toward the plunger 20 against the urging force of the spring 24 and pushes the plunger 20, so that the main flow paths 14 and 15 are pressed. Will be opened. Accordingly, the lift cylinder 3 contracts due to the weight of the fork 2, and the hydraulic oil discharged from the bottom chamber 3 a of the lift cylinder 3 is returned to the hydraulic pump motor 5 through the pilot check valve 9 to perform the cargo handling regeneration operation. It becomes.

  When the fork 2 is lowered, the hydraulic pump motor 5 is slightly rotated in the fork upward direction under the control of the controller 31. Then, the pressure between the hydraulic pump motor 5 and the pilot on-off valve 40, that is, the pressure in the pilot flow path 16 of the pilot check valve 9 decreases, and the pilot pressure is quickly released. For this reason, the poppet 22 of the pilot check valve 9 quickly moves to the lower lid portion 12 side by the biasing force of the spring 24, and accordingly, the plunger 20 quickly moves to the poppet 22 side by the biasing force of the spring 21. The main flow paths 14 and 15 are immediately closed.

  As described above, in the present embodiment, the pilot check valve 9 that opens and closes depending on the presence or absence of the pilot pressure is provided on the oil passage between the lift cylinder 3 and the hydraulic pump motor 5, and the hydraulic pump motor 5 and the tank 4. Is provided with a pilot on-off valve 40 that generates a pilot pressure when the hydraulic pump motor 5 is rotated in the fork lowering direction, and the generated pilot pressure is applied to the pilot check valve 9 through the pilot line 18. Like that. Therefore, similarly to the first embodiment, even if an expensive valve such as an electromagnetic valve or an electromagnetic proportional valve is not used and the control is complicated, the occurrence of operation shock and vibration at the start of lowering of the fork 2 is reduced. The downward movement of the fork 2 can be stabilized.

  In addition, by using the pilot on-off valve 40, the viscosity of the hydraulic oil does not change with the outside air temperature, and the ease of passage of the hydraulic oil does not change. Therefore, the pilot pressure is hardly affected by the outside air temperature. Can be generated.

  The present invention is not limited to the above embodiment. For example, in the above embodiment, all the hydraulic oil (return oil) discharged from the lift cylinder 3 is returned to the tank 4, but the invention is not limited to this, and a part of the return oil from the lift cylinder 3 is accumulated in an accumulator or You may supply to another hydraulic cylinder etc.

  Moreover, in the said embodiment, although the spring 24 is arrange | positioned between the base part 22a and the partition 23 of the poppet 22, such a spring 24 may not be in particular. In this case, when the rotation of the hydraulic pump motor 5 in the fork lowering direction is stopped, the poppet 22 moves to the lower lid 12 side by its own weight.

  In the above embodiment, the lifting device is mounted on a picking lift or the like. However, the lifting device of the present invention is not limited to such a picking lift, and may be applied to a counter-type forklift. At this time, as a hydraulic cylinder in the forklift, in addition to the configuration for raising and lowering the fork as in the above-described embodiment, a configuration in which an attachment such as a roll clamp is attached may be raised and lowered.

  Furthermore, the lifting device of the present invention is not limited to a forklift, and can be applied as long as the lowering operation is performed by its own weight, such as a hydraulic elevator.

  DESCRIPTION OF SYMBOLS 1 ... Lifting device, 2 ... Fork (lifting object), 3 ... Lift cylinder (hydraulic cylinder), 4 ... Tank, 5 ... Hydraulic pump motor (hydraulic pump), 6 ... Hydraulic piping (oil path), 9 ... Pilot check valve , 18 ... Pilot pipe (pilot pressure supply path), 20 ... Plunger, 21 ... Spring (first spring), 22 ... Poppet, 24 ... Spring (second spring), 26 ... Hydraulic pipe (oil path), 27 ... Orifice (pilot pressure generating means), 40 ... pilot on-off valve (pilot pressure generating means), 40a ... open position, 40b ... closed position, 42 ... spool, 48 ... spring.

Claims (5)

In the lifting device that lifts and lowers the lifting object by the hydraulic drive of the hydraulic cylinder,
A tank for storing hydraulic oil;
A hydraulic pump that sucks hydraulic oil from the tank and supplies the hydraulic oil to the hydraulic cylinder;
A pilot check valve disposed on an oil path between the hydraulic pump and the hydraulic cylinder, and allowing or blocking a flow of hydraulic oil from the hydraulic cylinder to the hydraulic pump according to the presence or absence of pilot pressure;
A pilot pressure generating means disposed on an oil passage between the hydraulic pump and the tank, and generating the pilot pressure when the hydraulic pump is rotated in a descending direction of the lift;
A lifting / lowering device comprising: a pilot pressure supply path for supplying the pilot pressure generated by the pilot pressure generating means to the pilot check valve.   The pilot check valve includes a plunger that opens and closes a flow path between the hydraulic pump and the hydraulic cylinder, and a first bias that biases the plunger in a direction to close the flow path between the hydraulic pump and the hydraulic cylinder. The lifting device according to claim 1, further comprising: a spring and a poppet that pushes the plunger to open a flow path between the hydraulic pump and the hydraulic cylinder when the pilot pressure is supplied. .   The elevating device according to claim 2, wherein the pilot check valve further includes a second spring that urges the poppet to the opposite side of the plunger. The pilot pressure generating means is an orifice for restricting hydraulic oil from the hydraulic pump,
The elevating device according to any one of claims 1 to 3, wherein the pilot pressure supply path is connected between an upstream side of the orifice and the pilot check valve. The pilot pressure generating means is a pilot opening / closing switchable between an open position that allows the flow of hydraulic oil from the hydraulic pump to the tank and a closed position that blocks the flow of hydraulic oil from the hydraulic pump to the tank. A valve,
The pilot open / close valve includes a spool and a spring that biases the spool to hold the spool in the closed position, and the open position and the closed valve according to a pressure between the hydraulic pump and the pilot open / close valve. Configured to move the spool between positions,
The elevating device according to any one of claims 1 to 3, wherein the pilot pressure supply path is connected between an upstream side of the pilot on-off valve and the pilot check valve.

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